Method for improving a polymerization reaction by taking out and analysing a sample

ABSTRACT

The invention relates to a device for taking out and analysing a sample from a polymerisation reactor comprising one or more sample conduits ( 2 ), for taking a sample out of said reactor and for conducting said sample to one or more sample flash tanks ( 3 ), whereby said conduits each are in communication with said reactor ( 19 ) and each are provided with at least two sampling valves ( 4, 5 ); comprising one or more sample flash tanks ( 3 ), for separating said solid particles and evaporated gas, whereby said sample flash tanks are connected to said conduits ( 2 ) and provided with means for analysing said evaporated gas ( 7 ), and comprising one or more sample receivers ( 6 ), for purifying said solid particles, whereby said receivers are connected to said sample flash tanks ( 3 ) and provided with means ( 8 ) for analysing said solid particles. The invention further relates to a method for improving a polymerisation reaction in a polymerisation reactor.

FIELD OF THE INVENTION

This invention relates to process control. In a first aspect, theinvention relates to a device for taking out and analysing a sample froma polymerisation reactor, in particular a polymerisation reactorsuitable for polymerising ethylene. In another aspect the inventionrelates to a method for improving a polymerisation reaction in apolymerisation reactor during a process for preparing bimodalpolyethylene.

BACKGROUND OF THE INVENTION

In a typical polymerisation reaction, monomer, diluent, catalyst,co-catalyst and optionally co-monomer and hydrogen are fed to a reactorwhere the monomer is polymerised. The diluent does not react but istypically utilised to control solids concentration and also to provide aconvenient mechanism for introducing the catalyst into the reactor. Thereactor effluent a mature of polymer, diluent, unreacted (co-)monomerand hydrogen, is removed from the reactor and fed to a flash tank wherethe polymer is separated from the diluent and unreacted (co-)monomer andhydrogen. Typically, catalyst will be contained in the polymer.

Polymerisation processes of ethylene may be carried out in loopreactors. In the polymerisation reaction of ethylene, differentreactants including the monomer ethylene, a light hydrocarbon diluentsuch as isobutane, a catalyst and optionally, a co-monomer such ashexene-1 and hydrogen are fed to a reactor. When polymerising ethylene,in the presence of a suspension of catalyst in diluent, said diluenthaving low solubility for the polymer, the polymer is produced in theform of solid particles, insoluble in the diluent. The contents of thereactor are circulated continuously with a pump to avoid deposition ofpolymer on the walls of the reactor. Slurry, consisting of the reactantsand polyethylene powder, is typically collected in one or more settlingslegs of the polymerisation reactor and discharged continuously to aflash tank, through flash lines, where most of the light hydrocarbondiluent and unreacted ethylene evaporates, yielding a dry bed ofpolyethylene in powder form. The powder is discharged to a purge drierin which the remaining light hydrocarbon and co-monomer are removed.Then the powder of polyethylene is transported to a finishing area wherevarious stabilisers and additives are incorporated. Finally it isextruded into pellets.

For obtaining polymer having suitable properties, it is essential In apolymerisation reaction to control the reaction conditions and inputcomponent quantities in the reactor. For doing so, it is conventional tosample the reactor contents and control several of the variables of theprocess in response with the analysis of the sample.

Several methods have been described to take samples from the reactorcontents. Generally the reactants in loop-type reactors are propelled atrelatively high velocities in order to maintain the catalyst andparticulate polymer produced in a suspended state and to preventdeposition or growing of polymer on the reactor walls. It is thereforenecessary that no vapor phase is present in the reactor where polymermight grow. In order to take a sample from such reactors, generally astandpipe is placed in the uppermost portion of the reactor to collectslurry. However, the slurry in said standpipe is generally not inequilibrium with the reactants, and hence it is almost entirelyimpossible to obtain a representative sample.

A vapor sample may be taken from the flash tank. However, sampling ofgases from flash tanks has several disadvantages. In polymerisationplants using flash tanks which are connected to a reactor by means offlash lines and settling legs, the settling legs themselves can presentproblems. Conventional settling legs have sections in which polymer cancollect while waiting for next dump cycle for transferring the slurry toa flash tank. The collected polymer can melt over time and deposit onthe inside walls of the settling leg. In addition, during collection ofthe slurry in the settling legs and before dumping it to the flash tank,the polymerisation reaction still continues. Also, there is a lag intime between recovery of slurry in the settling legs and furtherprocessing of the slurry to the flash tank. As a consequence thereof,reaction conditions, which are monitored after transfer of the slurry inthe flash tank, are different from the reaction conditions in thereactor. Analysis of a gas sample taken from the flash tank does notprovide updated information on the reaction conditions in thepolymerisation reactor and will result in an inaccurate analysis of thegas composition in the polymerisation reactor.

U.S. Pat. No. 3,556,730 refers to a sampling apparatus for taking asample comprising liquid, dissolved gas and suspended particulate solidsfrom a reactor into a fixed volume chamber. The reaction fluid in thechamber is then rendered non-reactive by immediately adding apredetermined volume of reaction termination fluid. The non-reactivesample is automatically discharged into a separation chamber from whichpart of the dissolved gas and liquid is continuously analysed.

U.S. Pat. No. 6,042,790 describes an apparatus and method formaintaining unreacted monomer concentration in a polymerisation reactor.In a polymerisation process utilising a high pressure flash to separatepolymer from unreacted monomer contained in the effluent stream from thereactor, the concentration of unreacted monomer in the reaction effluentis determined by withdrawing from the reactor an effective analysing amount of effluent, exposing the amount to a low pressure flash andanalysing the vaporised portion to determine the concentration ofmonomer. However, the described apparatus and method do not allow totake solid particles out of the reactor and to analyse these.

U.S. Pat. No. 4,469,853 provides a method for preparing polyolefins. Astep in this method consists of detecting the concentrations of olefinand hydrogen in the gas phase within the reactor by gaschromatography.However, the described apparatus and method do not allow to take solidparticles out of the reactor and to analyse these.

U.S. Pat. No. 6,037,184 discloses a method and apparatus for taking asample out of a flowing suspension formed by polymer particles andhydrocarbon diluent in a olefin polymerization process. The apparatusrelies on the use of a filter which is placed either straight to thewall of the loop reactor, whereby a sample is taken straight from theloop reactor, or in a transfer pipe which connects two loop reactors. Asample is taken out of the reactor and transferred to a vaporizingpressure reducer. The vaporized sample is then introduced in a waxseparation vessel and further in a wax removal vessel. However, thesample taken out of the loop reactor does not contain solid particles.Analysis of said sample is therefore not fully representative for thereaction conditions in the loop reactor. In addition, in embodimentswherein a sampling apparatus is provided In a transfer pipe whichconnects two loop reactors, reaction conditions, which are monitoredafter transfer of the slurry in the transfer pipe, are different fromthe reaction conditions in the loop reactor. Thus, analysis of a sampletaken from such transfer pipe does not provide fully updated informationon the reaction conditions in the polymerisation reactor.

A drawback in the above-described devices and methods is that they donot allow the control of several different variables of thepolymerisation process, such as e.g. monomer, co-monomer and hydrogen inthe gas phase and proper ties of the polymerisation product such as themelt flow index and density, in response with the analysis of thesample.

In addition, the above described methods and devices are not suitablefor controlling the polymerisation reaction in system wherein bimodalpolyethylene is prepared, i.e. in system comprising two interconnectedpolymerization reactors. In particular, the above-described methods anddevices do not provide for a representative sampling of a firstpolymerisation reactor in such bimodal system.

In view hereof, it is clear that there remains a need in the art forproviding a more accurate sampling system for taking and analysing asample from a polymerisation reactor. It is therefore an object of thepresent invention to provide a device cap able of taking out a samplefrom a polymerisation reactor and accurately analysing said sample. Itis further an object of the invention to provide a device capable oftaking out a sample from a polymerisation reactor, which consists of tworeactors being connected in series. Another object of the invention isto provide a sampling system for taking and analysing a sample from apolymerisation reactor wherein the solid as well as the gaseous phase ofsaid sample are analysed.

It is another object of the present invention to provide a method forimproving a polymerisation reaction in a polymerisation reactor. Inparticular, the invention aims to provide a method for improving apolymerisation reaction for preparing bimodal polyethylene in apolymerisation reactor, which consists of two reactors being connectedin series.

SUMMARY

In accordance with the present invention a sampling device is providedfor taking out and analysing a sample from a polymerisation reactorcontaining reactive fluid, said sample comprising solid particlessuspended in said reactive fluid. The device according to the inventioncomprises:

-   -   one or more sample conduits, for taking a sample out of said        reactor and for conducting said sample to one or more sample        flash tanks, whereby said conduits each are in communication        with said reactor and each are provided with at least two        sampling valves,    -   one or more sample flash tanks for separating said solid        particles and evaporated gas, whereby said sample flash tanks        are connected to said conduits and provided with means for        analysing said evaporated gas, and    -   one or more sample receivers for purifying said solid particles,        whereby said receivers are connected with said sample flash        tanks and provided with means for analysing said solid        particles.

In another aspect the invention relates to the use of a sampling deviceaccording to the invention for taking a sample out of a polymerisationreactor and for analysing said sample. Chemical and physical analysis ofsamples obtained from the reactor by use of a sampling device accordingto the present invention provide accurate and representative informationof the reaction conditions inside the reactor as well as the propertiesof the composition of the gas phase and the solid particles in thereactor. Because of the negligible residence time in the samplingdevice, samples taken by means of the present sampling device give anaccurate and representative picture of the conditions inside the reactorat sampling time.

In addition, the invention further relates to the use of the presentsampling device for improving a polymerisation reaction in apolymerisation reactor. The sampling device according to the presentinvention is usable for taking a sample from an individual reactor anddetermining the reaction conditions in said reactor. Preferably, samplesare analysed frequently, in order to accurately follow up thepolymerisation reaction in the reactor. Based on the analyses resultsobtained, one can adapt operational reaction parameters in the reactorin order to optimise the polymerisation reaction and to obtain a polymerhaving suitable properties and a desired product quality.

In addition, the sampling device according to the invention can also beused for improving a polymerisation reaction in a polymerisation reactorthat consists of two reactors that are connected to each other,preferably in series. Such reactor configuration advantageously allowsapplying different operational conditions in the different reactors,which allows playing on the properties of the final product. The problemin such reactor configuration however, consists of correctly determiningthe suitable moment on which a reaction product has certain desiredproperties and is suitable for being transferred from a first to asecond reactor and from the second reactor to means for furtherprocessing. Transfer of a reaction product having sub-optimal propertiesfrom such second reactor to further processing means considerablyreduces product quality. Using the sampling device according to thepresent invention in such configuration allows frequent analysis andfollow-up of the operational reaction conditions in both reactors. Thus,by frequently taking and analysing samples from a first and a secondreactor the present invention allows to adapt the reaction conditions inthe first as well as in the second polymerization reactor. Moreover, thesampling device according to the invention can also be used forimproving the polymerisation reaction conditions in a second slurry looppolymerisation reactor, by taking a sample out of a first slurry looppolymerisation reactor which is connected thereto, and by analysing saidsample. The suitable moment for transferring the reaction product fromthe second reactor to further processing can be correctly determined,and a final reaction product having optimal properties is supplied fromthe second reactor to further processing.

In another aspect, the present invention relates to methods forimproving a polymerisation reaction in a polymerisation reactor. Theterm “improving a polymerisation reaction in a polymerisation reactor”as used herein relates to the following up of a polymerisation reactionand the fine-tuning—if required—of operational reaction conditionsthereof in an individual reactor, in order to improve the efficiency ofthe polymerisation reaction and/or the product quality in thisindividual polymerisation reactor. This term also refers to thefollowing up of a polymerisation reaction and the fine-tuning—ifrequired—of operational reaction conditions thereof in two or morereactors which are connected to each other, preferably in series, suchthat the efficiency of the polymerisation reaction is ensured and that afinal reaction product resulting from the polymerisation reaction insaid reactors is fed at a suitable time and having optimal productquality to further processing means.

In an embodiment the present invention relates to a method for improvinga polymerisation reaction for preparing polyethylene in a slurry looppolymerisation reactor, said method comprising the steps of

-   -   a) taking a sample out of said reactor,    -   b) analysing said sample to determine said reaction conditions        in said reactor, and    -   c) based on results obtained in step b), adapt reaction        conditions in order to improve the polymerisation reaction in        said reactor.

In another embodiment, the present invention relates to a method forimproving a polymerisation reaction for preparing bimodal polyethylenein a first and in a second slurry loop polymerisation reactor which areconnected to each other, said method comprising the steps of

-   -   a) taking a sample out of said first reactor,    -   b) analysing said sample to determine said reaction conditions        in said first reactor, and    -   c) based on results obtained in step b), adapt reaction        conditions in said first reactor and in said second reactor in        order to improve the polymerisation reaction in said first        reactor and in said second reactor.

In another preferred embodiment, the invention relates to a method forpreparing bimodal polyethylene in a first and in a second slurry looppolymerisation reactor, comprising the steps of

-   -   a) taking a sample out of said first reactor,    -   b) analysing said sample to determine said reaction conditions        in said first reactor,    -   c) based on results obtained in step b), adapt reaction        conditions in said first reactor in order to provide an        optimised reaction product in said first reactor,    -   d) transferring said reaction product from said first reactor to        said second reactor,    -   e) optionally, based on results obtained in step b), adapt        reaction conditions in said second reactor in order to provide        an optimised reaction product in said second reactor, and    -   f) feeding at a suitable time said optimised reaction product        from said second reactor to further processing means.

In another embodiment, the invention relates to a method for optimisingthe polymerisation reaction conditions for preparing bimodalpolyethylene in a second slurry loop polymerisation reactor, connectedto a first slurry loop polymerisation reactor, comprising:

-   -   a) taking a sample out of said first slurry loop polymerisation        reactor,    -   b) analysing said sample, and    -   c) based on results obtained in step b), adapt reaction        conditions in said second reactor in order to provide an        optimised reaction product in said first reactor.

In particular, in a preferred embodiment, the step a) in these methodsof taking a sample comprises

-   -   providing a sample from said first reactor to a sample flash        tank, by transferring said sample through a conduit connecting        said first reactor to said sample flash tank,    -   separating in said sample flash tank solid particles from        evaporated gas in said sample by controlling the pressure in        said flash tank,    -   supplying said solid particles from said sample flash tank to        one or more sample receivers, by transferring said solid        particles through a conduit connecting said sample flash tank        and said sample receivers, and    -   purifying said solid particles in said sample receivers, by        degassing and drying.

Furthermore, in another preferred embodiment the analysis step b) in thepresent method comprises analysing evaporated gas obtained from saidsample flash tanks with analysing means, and analysing solid particlesobtained from said sample receivers with analysing means.

In another preferred embodiment of said method, said sample is taken outof a reactor part and analysed by means of a sampling device accordingto the present invention.

The sampling device and the method according to the invention areparticularly useful in the polymerisation process of ethylene. Thoseskilled in the art will immediate recognise the many other effects andadvantages of the present method and device from the detaileddescription and accompanying drawings provided below.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 represents a schematic view of an embodiment of a sampling deviceaccording to the present invention.

FIG. 2 is a schematic representation of a polymerisation reaction andrecovery system, which utilises a sampling device according to thepresent invention.

FIG. 3 shows the effect of using the present invention for controllingpolymerisation conditions for a bimodal polyethylene.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described in terms of the polymerisation of ethylene.Suitable “ethylene polymerisation” includes but is not limited tohomo-polymerisation of ethylene, co-polymerisation of ethylene and ahigher 1-olefin co-monomer such as butene, 1-pentene, 1-hexene, 1-octeneor 1-decene. More in particular, the present invention is described interms of the polymerisation of ethylene for manufacturing bimodalpolyethylene (PE). “Bimodal PE” refers to PE that is manufactured usingtwo reactors, which are connected to each other in series. However, theinvention is applicable to any polymerisation reaction where it isdesired to take and analyse a sample from a polymerisation reactor In anaccurate way, or to improve the polymerisation reaction in the reactor.

In a preferred embodiment, ethylene polymerisation comprises feeding toa reactor the reactants including the monomer ethylene, a lighthydrocarbon diluent, a catalyst and optionally a co-monomer andhydrogen. In an embodiment of the present invention, said co-monomer ishexene and said diluent is isobutane.

As used herein, the term “polymerisation slurry” or “polymer slurry” or“slurry” means substantially a two-phase composition including polymersolids and liquid. The solids include catalyst and a polymerised olefin,such as polyethylene. The liquids include an inert diluent, such asisobutane, with dissolved monomer such as ethylene, co-monomer,molecular weight control agents, such as hydrogen, antistatic agents,antifouling agents, scavengers, and other process additives.

In a first aspect, the present invention relates to a sampling devicefor taking out and analysing a sample from a polymerisation reactor.Referring to FIG. 1, there is illustrated an embodiment of a samplingdevice 1 according to the invention. In a particularly preferredembodiment, the sampling device 1 according to the invention consists oftwo conduits 2, each connected to one sample flash tank 3, which isconnected to two sample receivers 6, as illustrated on FIG. 1. However,it is clear that the present device may contemplate more conduits,sample flash tanks and/or sample receivers. It is dear from the presentdescription that numbers of dimensions of the different parts of thesampling device can be related to the sise of the polymerisationreactors and can be changed in function of the reaction sises.

The term “sample” as used herein refers to a slurry sample that is takenout of the reactor. In the sample flash tank, most of the lighthydrocarbon diluent, unreacted ethylene and co-monomer evaporates and isremoved from the sample flash tank. A portion of the removed gas istaken for analysis. The solids, i.e. polyethylene in powder form,remaining in the sample flash tank are transferred to sample receiversin which remaining light hydrocarbon and co-monomer is removed and theresulting polyethylene powder is analysed. Thus, according to thisinvention, the sample is separated in a gas and a solid phase, which areboth analysed.

Technically speaking, as used herein the terms “a reactor” or “a part ofa reactor” are to be considered as equivalents. In view hereof, it shallbe understood that embodiments of the present invention referring to afirst and a second polymerisation reactor which are connected to eachother, may also refer to embodiments referring to a first part and asecond part (different from the first part) of a single polymerisationreactor. This means that embodiments of the invention referring to afirst and a second polymerisation reactor which are connected to eachother, and wherein a sample is taken out a first reactor and analysed inorder to adapt the operational conditions of a second reactor, may alsorefer to embodiments wherein a sample is taken out of a first part of asingle reactor and analysed in order to adapt the operational conditionsin another part of said single reactor.

The device comprises one or more sample conduits 2, for taking a sampleout of said reactor. An effective analysing amount of slurry is removedvia two conduits 2 from a polymerisation reactor 19. In FIG. 1, it isillustrated that a sample is obtained from two separate reactors 19, 20,which are not interconnected. In a preferred embodiment said reactorsconsist of liquid full loop reactors. Loop reactors are known in the artand need not be described herein in detail. However, it should beunderstood that the present device can also be applied to take samplesof reactors, in particular liquid full loop reactors, which areconnected in series, as illustrated on FIG. 2. In a more preferredembodiment the device can be used on a polymerisation reactor comprisinga first 19 and a second reactor 20 which are interconnected in series byone or more settling legs 21 of the first reactor 19 connected fordischarge of slurry from the first reactor 19 to said second reactor 20,as illustrated on FIG. 2.

The sampling device according to the present invention may be placed atone of the elbows of the loop reactor or at other places. Preferably,the device 1 is positioned on an elbow of the reactor, but not in theproximity of the pump for continuously circulating the contents of thereactor through the reactor loops. For instance, on one of the elbows ofsuch loop reactor 19, 20, one or more conduits 2 can be provided forremoving a sample from the reactor and transferring such sample to asample flash tanks 3. The conduits 2 each are in communication with saidreactor 19, 20 and the sample flash tank 3. Several conduits may beprovided which can be used separately or simultaneously.

In a preferred embodiment, the conduits 2 are provided with at least twosampling valves 4, 5. The valves are preferably placed as close to thereactor as is possible due to the limitations of valve sise, fittings,etc. Preferably, between the valves 4 and the reactor 19, 20, flushingmeans are provided In order to avoid plugging and blocking of theconduit part between the valves 4 and the reactor 19, 20.

The conduits 2 are provided with means for periodically sequentiallyopening and closing said valves 4, 5. The mechanism of dosing andopening the valves 4, 5 is as follows: first the first valve 4 is openedwhile maintaining said second valve 5 closed, then said first valve 4 isclosed while maintaining said second valve 5 closed, subsequently, thesecond valve 5 is opened while maintaining said first valve 4 closed andfinally, said second valve 5 is closed while maintaining said firstvalve 4 closed. According to this mechanism, the valve closest to thereactor 4 is open while the second valve 5 is closed. The volume betweenthe two valves is filled with slurry coming from the reactor. The valvenear the reactor 4 is closed and the second valve 5 is opened. As thepressure is lowered, the slurry flashes and pushes the product to asample flash tank 3. Valve 4 is open only long enough to take asufficient sised sample such that analytical error is minimised.Preferably the sequence of opening and closing the valves 4, 5 followsfixed time limits. By way of illustration, a suitable sequence ofopening and dosing the valves may comprise opening of the valve 4between two and ten seconds, and preferably for four seconds, whilekeeping valve 5 closed; followed by closing the first valve 4 betweenone and five seconds, and preferably for two seconds while keeping thesecond valve 5 closed; opening the valve 5 between two and twentyseconds, and preferably for six seconds, while valve 4 remains closedand closing the valve 5 between one and sixty seconds, and preferablyfor five seconds while keeping the valve 4 closed. After this sequence,the sequential mechanism can be repeated.

The sise of the sample is determined by the volume of pipe, whichextends between valve 4 and valve 5, which is closed during the samplingof the reactor. Typically, an effective analysing amount will be a minorvolume proportion of the amount produced by the polymerisation reactor.In a preferred embodiment, the sise of the sample volume is adapted byproviding different conduits lengths and thus different volumes of pipeextending between valve 4 and valve 5. According to the presentinvention, taking a relative small amount of sample from said reactorprovides reliable data on the polymerisation reaction in the reactor.

A small amount of sample in this invention means the smallest possibleamount of material that it is technically feasible to withdraw.Accordingly, the size of the sample flash tank is less than 10%,preferably less than 1%, more preferably less than 0.1% of that of asingle flash tank of a size adapted to that of the reactor.

In addition, the device provides additional flushing valves 38, providedon the conduit downstream the first valve 4 and upstream the secondvalve 5. These valves 38 play a role in an automatic flushing mechanism,which is activated after taking a sample from the reactor. Automaticflushing enables cleaning and rinsing of the sample volume In theconduit with diluent, in particular isobutane, and keeps the conduitfree.

When taking a sample from the reactor, the sequential opening/dosingmechanism of the valves 4, 5 is activated. Interruption of saidsequential mechanism stops sample out take and activates the automaticflushing mechanism. During automatic flushing the first valve 4 remainsopen together with the flushing valve 38, in order to provide continueflushing to the reactor such that plugging is avoided. The flushingvalve 38 is always closed prior to opening valve 5. By way ofillustration, a suitable sequential mechanism for activating theautomatic flushing mechanism is as follows: the first valve 4 is closed,the flushing valve 38 is closed and the second valve 5 is opened,preferably for ten seconds, and subsequently closed again. The flushingvalve 38 is then opened, between five and thirty seconds, and preferablyfor fifteen seconds and closed again. The second valve 5 is subsequentlyre-opened, preferably for ten seconds and then closed. The flushingvalve 38 is opened and remains open, while also the first valve 4 isopened and remains open.

When a novel sample needs to be taken out of a reactor, the automaticflushing mechanism needs to be interrupted, which preferably takes placeas follows: the flushing valve 38 is closed and remains closed, thefirst valve 4 is closed. The second valve 5 is opened during preferablyten seconds and closed again, while the flushing valve 38 is closed.After preferably twenty to thirty seconds, the sequential mechanisms ofopening and closing the valves 4, 5 as described above, can bere-activated in order to obtain a sample in the conduit volume providedbetween said valves 4, 5.

When the valves 4 near the reactor 19 are opened, the sample isintroduced in the conduit 2 and a sample volume is further transportedto the sample flash tank 3, by means of sample flash lines 22. In apreferred embodiment, the slurry is provided at the entrance of thesample flash tank at a suitable temperature and pressure, such that theslurry is entered into the sample flash tank in gas form.

Preferably the pressure in reactor 19 is around 43 bars. In the sampleflash lines, the pressure is reduced in order to reach a pressurepreferably comprised between 1.1 bar and 3 bar in the sample flash tank3. The major drop in pressure preferably takes place at the second valve5, and is further linearly reduced between the second valve 5 and thesample flash tank 3 in the flash lines 22.

In a preferred embodiment, said sample flash lines 22 are constructed asjacketed pipes, i.e. double envelope tube exchangers. The sample flashlines 22 consist of an inner tube for transporting the sample, and anouter tube, provided as a coat on said inner tube, which can be heated,e.g. by means of a steam stream flowing through said outer tube. Heatingof the sample improves and facilitates further purification of thesample and increases the degassing efficiency in the sample flash tank,which guarantees a reliable and accurate gas analysis. Preferably thesise of the sample flash lines 22 is chosen in order to have the slurryat a correct temperature entering the sample flash tank 3. The sise ofthe sample flash lines 22 is also chosen in order to obtain a suitablevelocity of the slurry. The temperature in the coating tube ispreferably regulated by adapting steam pressure by means of steampressure controlling means 23. It is preferred that the temperature inthe sample flash tank is at least higher than 35° C. and preferablyhigher than 50° C.

The slurry transferred through conduit 2 and 22 is provided to a sampleflash tank 3 wherein a more complete separation between the polyethyleneand the unreacted reactants including ethylene, hexene, hydrogen andisobutane occurs. Preferably, said sample flash tank 3 consists of atubular body 9 and a conical bottom 10.

Providing a suitable temperature and pressure in the sample flash tank 3enables to increase the degassing efficiency in the sample flash tankand to obtain a substantially degassed polyethylene powder remaining inthe tank. Increased degassing efficiency also permits to increase theaccuracy of the gas analysis performed on a portion of the gas removedfrom the sample flash tank. The sample flash tank 3 is heatable. Thetubular body 9 is provided with a heatable coat 39 and the conicalbottom 10 is preferably provided on its surface with conduits 11 whereinsteam or hot water can be provided. Preferably, the temperature in thesample flash tank is higher than 35° C., and even more preferred, higherthan 50° C. The pressure in the sample flash tank 3 will vary dependingon the nature of the diluent and monomer and the temperature selected.Preferably, according to the present invention, the pressure value inthe sample flash tank 3 comprises between 1.1 and 3 bar and morepreferred between 1.5 and 1.6 bar. In the sample flash tank 3 freeunreacted ethylene, isobutane, hexene co-monomer and hydrogen arereleased as vapor; any hydrocarbons trapped in the pores of the polymerpowder are carried away.

Flash gas, comprising essentially unreacted ethylene, isobutane, hexeneco-monomer and hydrogen, is removed from the sample flash tank 3 througha conduit 24, preferably provided at the top of the sample flash tank 3.Means 26 are preferably provided on conduit 24 which regulate thepressure in said conduit such that the pressure is higher upstream themeans 26 than downstream the means, in order to avoid reflux of thegases from the reactor, which could induce a deficient off gas analysis.Preferably, the pressure from the sample flash tank is used as control,and the means 26 installs a pressure, which preferably exceeds the flashtank pressure with 100 mbar.

The flash gas, which is a mixture of unreacted reactants, is preferablytransferred to a recycle section 31, wherein the gas is compressed, thereactants are separated from the mixture, and fed to the polymerisationreactor if desired at a suitable flow rate.

A sample of the fluid (gas) flowing through the conduit 24 is providedto a gas analyser 7 through conduit means 25. Samples taken from thevapor phase are indicative of the compositions in the vapor phaseexisting in the reactor. The analyser 7 is preferably a chromatographicanalyser. The analyser 7 provides an output signal, which isrepresentative of the concentration of one or several reactants in thefluid flowing through conduit 24. Essentially, this signal isrepresentative of the concentration of unreacted ethylene, hexene, andhydrogen removed from reactor 19. The signal can be provided from theanalyser 7 as an input to a computer. In response to this signal, thecomputer may determine the concentration of unreacted ethylene, hexene,and hydrogen in the reactor 19 and determines whether adjustment ofethylene, hexene, and hydrogen flow to the reactor 19 is needed.Additionally, instead of adjusting these feeds, the system also could beset up so that other or additional reactants such as diluent (isobutane)feed or catalyst feed are adjusted in response to a signal from thecomputer.

A solid fraction or powder essentially consisting of PE and dissolvedisobutane and co-monomer is collected at the bottom of the sample flashtank 3 from which it is transferred to sample receivers 6 for furtherpurification. Transfer of the powder is done by means of a conduit 12,provided with at least two valves 13, 14. Said conduit 12 is preferablyprovided with means for periodically sequentially opening said firstvalve 13 while maintaining said second valve 14 closed, closing saidfirst valve 13 while maintaining said second valve 14 closed, openingsaid second valve 14 while maintaining said first valve 13 closed andclosing said second valve 14 while maintaining said first valve 13closed. This mechanism allows a well-defined amount of powder to betransferred to the sample receiving means 6. The valves also avoid theentrance of nitrogen, provided downstream in the system, into the sampleflash tank 3. Preferably, the sampling device is further provided withmeans 27 for purging with wet nitrogen, preferably downstream the secondvalve 14 on conduit 12. Providing wet nitrogen enables to kill residualalkyl and catalyst in the powder.

Powder removed from the sample flash tank 3 through conduit means 12will be treated to remove any remaining co-monomer and diluent suchtreatments preferably include degassing and drying in a sample receiver6. Preferably, said sample receiver 6 consists of a tubular body 15 anda conical bottom 16. The sample receiver 6 is heatable. The conicalbottom 16 is preferably provided on the surface with conduits 11 whereinsteam or hot water is provided. It is preferred to heat up the receiversin order to increase the degassing efficiency and purification in thesample receiver. Preferably, one sample flash tank 3 may be connected toseveral sample receivers 6 by means of the conduit 12. In order toalternately send powder to the one or the other receiver 6, a diverter18 is provided, downstream the second valve 14 and upstream of thesample receivers 6 on said conduit 12.

Generally, PE powder is collected in one sample receiver 6, which is inconnection with means 8 for analysing said polymer powder. If it isnecessary to take a sample for analysis, or to switch to anotherreceiver 6, e.g. when one of the receivers is full and needs to beemptied, the PE powder can be directed, by regulation of the diverter18, to a second sample receiver, while the first receiver can at themeantime be drained. Subsequently, the flash tank is again connected tothe first receiver, and from the second receiver a sample can be takenfor analysis.

In particular, the purpose of the sample receivers 6 is to striphydrocarbons trapped in the pores of the polymer. This is preferablydone with a long residence time in the receiver and a nitrogen sweep.The sample receivers 6 comprise means 28 for providing nitrogen,preferably at the bottom of said receiver 6. Providing nitrogen to thereceiver enables to further purge and purify the PE powder in thereceiver 6. Nitrogen flushed in the receivers can be removed by means ofa conduit 29 to a collecting vessel 30, e.g. seal oil pot, which may becommon for two or several sample receivers 6. From this collectingvessel, nitrogen is released to the atmosphere. In addition, the samplereceivers 6 can be further provided with means for measuringexplosiveness.

In another preferred embodiment, the sample receivers 6 are providedwith a filter 17, preferably at the top of the tubular body 15 of thereceivers 6, for avoiding powder fines to be swept away with the conduit29 releasing nitrogen. These filters preferably are bag filters having anitrogen pulse jet for cleaning.

The sampling device according to the present invention comprises severalprotection mechanisms in order to correctly and efficiently controloperations of the sampling device. For instance, when the pressurebecomes too high in the sample flash tank or when a high level isreached in the sample flash tank, the sampling sequential mechanism isstopped and automatic flushing is activated. When a very high pressureis obtained in the sample flash tank, the valves 4, 5 and the flushingvalves 38 are closed. In another example, one sample receiver can bedrained and emptied, when the diverter 18 is oriented towards anothersample receiver, provided explosiveness is sufficiently low. Anothercontrol system consists of diverting the transfer of PE powder from thesample flash tank 3 to another sample, receivers 6 when a high level isobtained in a first sample receiver. The transfer of PE powder from thesample flash tank 3 to the sample receivers 6 via conduit 12 can beinterrupted in case of a high pressure in the sample flash tank 3 or ahigh level in the sample receivers 6. Another control system consists ofclosing the conduit to the gas analyser 7 in case a high pressure isobtained in the sample flash tank 3. Furthermore, when a low pressure isregistered in the polymerisation reactor 19, the sampling sequencemechanism is stopped and automatic flushing is activated.

Referring now to FIG. 2, a schematic representation of a polymerisationreaction and recovery system, which utilises sampling devices accordingto the present invention, is illustrated. The figure shows two liquidfull loop reactors, comprising a first 19 and a second reactor 20connected in series by one or more settling legs 21 of the first reactorconnected for discharge of slurry from the first reactor 19 to saidsecond reactor 20. Such configuration can be applied for manufacturingbimodal PE. Each reactor 19, 20 is provided with a sampling device 1according to the invention. Preferably, in case two reactors are used,the pressures in the first reactor 19, is preferably comprised between43 and 44 bar, while the pressure in the second reactor comprisesbetween 41 and 42 bar. The pressure is generally lower in the secondreactor compared to the first reactor to ensure a sufficient flow rate.

The process for manufacturing bimodal PE is known in the art and forinstance disclosed in U.S. Pat. No. 5,639,834, which describes a processfor the co-polymerisation of ethylene in two liquid full loop reactorsin series wherein high and low average molecular weight polymers areproduced respectively in a first and a second reactor. The reactionconditions in the first and the second reactors are different in orderto obtain high and low average molecular weight polymers respectively inthe first and second reactor. The ethylene polymer stream obtained inthe first reactor is transferred to the second loop reactor through oneor more setting legs of the first reactor, e.g. using six settling legseach one being independently filled with reactor slurry, solids beingconcentrated by gravity setting, and discharged.

For taking a sample of slurry that is produced in the reactors 19, 20 insuch configuration, for off gas analysis and determination of thecharacteristics of the produced gas composition and PE powder, aspecific sampling device according to the present invention is providedon the first reactor 19 or on both the first 19 and the second reactor20, as illustrated on FIG. 2. However, it should be clear that thesampling device according to the present invention is also very suitablefor use on individual reactors for manufacturing polyethylene, or onreactors for manufacturing of monomodal PE. “Monomodal PE” is producedusing two reactors, which are operating in parallel. In accordance withsuch reactors, the sampling device according to the present inventioncan be provided on both reactors.

As illustrated on FIG. 2, the following reactants are provided topolymerisation reactor 19: ethylene, hexene-1 co-monomer, isobutanediluent, a catalyst and hydrogen. The several reactants can beintroduced to the reactor by means of one or several conduits. Themajority of the reaction effluent, i.e. polymerisation slurry, isremoved from the reactor 19 by one or more settling legs 21 of the firstreactor and discharged from the first reactor 19 to said second reactor20. A sampling device 1 according to the invention is connected to saidfirst reactor 19. Slurry removed through conduit means 2 and 22 isprovided to a sample flash tank 3. In the sample flash tank 3vaporisation of the monomer, co-monomer, hydrogen and diluent occurs;however, vaporisation can also occur at least partially within conduit22. Unreacted reactants are removed from sample flash tank 3 throughconduit means 24. A sample of the gas flowing through conduit means 24is provided to an analyser 7, preferably a chromatographic analyser. Theremaining gas flowing through conduit 24 can be recycled by means of arecycle section 31, and the separated reactants can be fed, to thepolymerisation reactor 19 if desired. Solid polyethylene is providedfrom the sample flash tank 3 through conduit means 12 to a samplereceiver 6. The reaction conditions in the first reactor are monitoredby means of a sampling device according to the present invention. Basedon the results obtained from this analysis, the reaction conditions inthe first reactor are adapted in order to obtain an optimal reactionproduct leaving the first reactor 19.

Slurry is transferred from the first 19 to the second reactor 20 bymeans of lines 40. Transfer of slurry from one to another reactor ispreferably continuously performed by using the settling legs 21.

The second reactor 20 is further connected by means of flash lines 32 toa flash tank 33. unreacted reactants are separated from the incomingslurry in said flash tank 33. Polyethylene powder is removed from thetank 33 through conduit means 34 which conduct the polyethylene powderto a purge column 36. Within the flash tank 33 unreacted reactants areremoved as vapor from flash tank 33 via conduit 35. The gas flowingthrough conduit 35 can be transferred to a recycle section 31, where thereactants in the gas are separated and if desired again fed to thepolymerisation reactor 19. The conduit 35 can be further provided with agas analyser 7 for analysing a portion of the gas flowing through saidconduit 35. PE powder removed from the flash tank 33 will be furthertreated to remove any remaining co-monomer and diluent by providing itto a purge column 36, where after PE is further removed through conduitmeans 37. Analysis of the PE powder can be done by means of analysingmeans 8 which a re provided in connection to conduit 34 or to conduit37. Preferably, means 8 provided in connection to conduit 34 areutilised when the residence time in the purge column 36 is long, whilemeans 8 provided in connection to conduit 37 can be utilised when theresidence time in the purge column 36 is short.

Again, a sampling device according to the invention can be connected tosaid second reactor 20, in order to take a sample and analyse a samplefrom the second reactor 20. Slurry removed through conduit means 2 and22 is provided to a sample flash tank 3. Unreacted reactants arevaporised and removed from sample flash tank 3 through conduit means 24.A sample of the gas flowing through conduit means 24 can be provided toa gas analyser 7, preferably a chromatographic analyser. The remainingfluid flowing through conduit 24 can be compressed and recycled back tothe polymerisation reactor 19 or 20 after passage through a recyclesection 31 if desired. PE powder is provided from the sample flash tank3 through conduit means 12 to a sample receiver 6 for furtherpurification.

In another preferred embodiment, it is to be understood that wherenecessary flushing and purging means and lines are available on thesampling device according to the invention in order to avoid plugging,blocking or explosiveness risk.

With reference to FIG. 2, it should be noted that the sample flash tank3 and the sample receivers 6, preferably have a similar configuration asthe flash tank 33 and the purge column 36, respectively, but arerelatively much smaller than the flash tank 33 and the purge column 36.In a preferred embodiment, the sample flash tank 3 and the samplereceivers 6 are at least 10 times, and preferably 100 times and evenmore preferred 1000 times smaller than the flash tank 33 and the purgecolumn 36. This indicates that according to the invention small volumesof samples, preferably around 40 cm³, are sufficient to provide accurateand reliable data on the reaction in a reactor.

In another aspect the present invention relates to a method forimproving a polymerisation reaction in a polymerisation reactor. In oneaspect the method comprises the improvement and optimisation of apolymerisation reaction in an individual polymerisation reactor. In anembodiment said method comprises the steps of

-   -   a) taking a sample out of said reactor, preferably by means of a        sampling device according to the present invention.    -   b) analysing said sample to determine said reaction conditions        in said reactor, and    -   c) based on results obtained in step b), adapt reaction        conditions in order to improve the polymerisation reaction in        said reactor.

In another aspect, the method comprises the improvement and optimisationof a polymerisation reaction in a polymerisation reactor, which consistsof several parts or several reactors, which are connected to each otherin series. Preferably said polymerisation reaction comprises thepolymerisation of ethylene to prepare bimodal polyethylene in a firstand a second reactor which are connected to each other. Said methodcomprises the steps of

-   -   a) taking a sample out of said first (part of said ) reactor 19    -   b) analysing said sample to determine said reaction conditions        in said first (part of said) reactor 19,    -   c) based on results obtained in step b), adapt reaction        conditions in said first and second (parts of the said) reactor        in order to improve the polymerisation reaction in said first        and second (parts of said) reactor.

In a preferred embodiment, said method comprises the steps of

-   -   a) taking a sample out of said first (part of said) reactor 19,    -   b) analysing said sample to determine said reaction conditions        in said first (part of said) reactor 19,    -   c) based on results obtained in step b), adapt reaction        conditions In said first (part of said) reactor 19 In order to        provide an optimised reaction product in said first (part of        said) reactor, and    -   d) transferring said reaction product from said first (part of        said) reactor 19 to said second (part of said) reactor 20,    -   e) optionally, based on results obtained In step b), adapt        reaction conditions in said second (part of said) reactor in        order to provide an optimised reaction product in said second        (part if said) reactor, and    -   f) transferring at a suitable time said optimised reaction        product from said second (part of said) reactor 20 to further        processing means.

In a particularly preferred embodiment, the method comprises providing areactor wherein said first part and said second part of saidpolymerisation reactor consists of a first 19 and a second 20 liquidloop reactor, connected to each other in series, wherein the firstreactor 19 has one or more settling legs 21 for discharge of slurry fromthe first reactor 19 to said second reactor 20. The method isparticularly suitable for being applied for improving a polymerisationreaction in a polymerisation reactor during a process for preparingbimodal polyethylene. For preparing bimodal polyethylene, twopolymerisation reactors are used that are connected to each other inseries, as e.g. illustrated on FIG. 2.

The present invention provides a method for monitoring and optimisingthe operational conditions in a first reactor in the polymerisationprocess for obtaining polyethylene. The method consists of taking asample taken out of reactor, analysing said sample to determine theoperation reaction conditions in the first reactor. A sampling deviceaccording to the invention is preferably provided on said first reactorand enables to analyse a sample from said reactor and to determine thereaction conditions in the first reactor. Based on the analyses resultsobtained, one can adapt or fine-tune the operational reaction parametersin the first reactor if required, in order to improve the polymerisationreaction in said reactor and to obtain polyethylene having the desiredproperties.

Preferably, sampling is performed continuously and the samples areanalysed frequently, in order to accurately follow up the polymerisationreaction in the first reactor. Analysis of these samples is preferablydone at defined time points. Preferably, a PE powder sample obtainedfrom the sample receivers 6 is analysed every one or two hours, and agas sample, obtained from the sample flash tank 3 is analysedautomatically every five to fifteen minutes.

In another embodiment, the sampling device according to the inventioncan be provided on both a first and a second reactor. By additionallyproviding a sampling device according to the invention on the secondreactor, samples from said second reactor can be continuously taken andfrequently analysed and one is capable of following up the reactionconditions and the polymerisation reaction in the second reactor, andadapt operational reaction parameters if required, to improve thepolymerisation reaction and to obtain an end product having the desiredproperties. Once the reaction product of the first reactor has beentransferred to the second reaction the method may further comprisetaking a sample out of the second reactor, analysing said sample todetermine said reaction conditions in said second reactor and based onresults obtained on the reaction conditions, fine-tune and adapt thereaction conditions in the second part of said reactor in order toprovide a optimised reaction product as a result of the reaction in saidsecond part of in said reactor.

The method further allows determining the suitable moment fortransferring the reaction product having optimal desired properties tofurther processing means. Transfer of a reaction product having optimalproperties at an optimal moment for further processing, considerablyimproves the quality of the obtained reaction product

The different properties of the polyethylene (molecular weight, density,. . . ) can be adjusted by controlling operating parameters of thereactors such as temperature, ethylene concentration, hexeneconcentration, hydrogen concentration, residence time. Other reactorparameters could be controlled as well, such as reactor pressure, solidconcentration inside the reactor and catalyst productivity, powderproperties, etc. . . .

In another preferred embodiment, the method comprises taking a specificvolume of a sample from said first part 19 of said reactor. This can beobtained by using a specific sampling mechanism. The method consists ofproviding valves 4, 5 on conduits 2 connecting the reactor 19 with asample flush tanks 3, having means for periodically sequentially openingand dosing said valves 4, 5. The mechanism of dosing and opening thevalves 4, 5 is described in more detailed above. The sise of the sampleis determined by the volume of pipe, which extends between valve 4 andvalve 5.

In a further embodiment, the present invention relates to a method,wherein step a) wherein a sample is taken comprises

-   -   providing a sample from said first part 19 of said reactor to a        sample flash tanks 3, by transferring said sample though a        conduit 2 connecting said first part 19 of said reactor to said        sample flash tank 3,    -   separating in said sample flash tank 3 solid particles from        evaporated gas in said sample by controlling the pressure in        said flash tank 3,    -   supplying said solid particles from said sample flash tank 3 to        one or more sample receivers 6, by transferring said solid        particles though a conduit 12 connecting said sample flash tank        3 and said sample receivers 6, and    -   purifying said solid particles in said sample receivers 6, by        degassing and drying.

In addition, in another further embodiment, the step b) in the presentmethod comprises analysing evaporated gas obtained from said sampleflash tanks 3 with analysing means 7, and analysing solid particlesobtained from said sample receivers 6 with analysing means 8.

While the invention has been described in terms of the presentlypreferred embodiment, reasonable variations and modifications arepossible by those skilled in the art and such variations are within thescope of the described invention and the appended claims.

EXAMPLE

The following example illustrates the effectiveness of the presentinvention in better controlling polymerisation conditions andsubsequently polymer properties. The reactor used herein is a commercialdouble loop reactor with the two loops in sequential configurationequipped with a sampling system as described in the present document.The reactor is used to produce a bimodal polyethylene resin.Polymerisation conditions are controlled on both reactors to ensuresuitable product properties.

FIG. 3 shows the effects of using the sampling system of the presentinvention for controlling polymerisation conditions on the melt flowindex of a bimodal polyethylene. FIG. 3 displays the evolution of thescaled melt index over time. The scaled melt index is calculated aftercompletion of the production run in the following way: From the meltflow indices measured during the first 21 hours an average melt flow iscalculated. The scaled melt flow index (“MI fluctuations”) is thequotient of the actual real melt flow and the averaged melt flow indexof the first 21 hours. For a perfectly controlled system the quotientassumes a value of 1.

In FIG. 3 the first 21 hours show the evolution of the scaled melt flowindex when the sampling system of the present invention was in use. Theuse of the sampling system permits to control the melt flow index of thebimodal polyethylene within very narrow specifications.

After 21 hours the sampling system of the present invention was turnedoff. This immediately led to a significant increase in the fluctuationof the melt flow index in the bimodal polyethylene.

The data clearly shows that the sampling system of the present inventionallows for better control of polymerisation conditions and consequentlyof final product properties.

1-24. (canceled)
 25. In a system for the recovery of a polymer samplefrom a polymerization reactor comprising: a) a polymerization reactorfor the polymerization an olefin polymer in a liquid diluent comprisingb) a sample conduit connected to said polymerization reactor forreceiving a sample of polymer particles in said liquid diluent from saidpolymerization reactor; c) a sample release valve in said conduit; d) aflash tank associated with said conduit effective for the separation ofsaid diluent from polymer particles and having an inlet connectedthrough a flash line to the outlet of said sample release valve, a firstoutlet for the removal of polymer particles from said flash tank and asecond outlet for the release of gas from said flash tank; e) a samplereceiving chamber having an inlet for receival of a polymer sample andan analyzer for analyzing the contents in said sample receiving chamber;and f) a sample transfer line extending from said flash vessel to saidsample receiving chamber and provided with at least one valve with theoutlet of said valve connected to said sample receiving chamber.
 26. Thesystem of claim 25 wherein said sample conduit comprises a sample inputvalve spaced from said sample release valve in the direction of saidreactor.
 27. The system of claim 26 further comprising a line connectedto said sample conduit between said sample release valve and said sampleinput valve to provide for the introduction of a flushing liquid to saidconduit.
 28. The system of claim 26 wherein second outlry of said flashtank is provided with a gas release line for the removal of gas fromsaid flash tank.
 29. The system of claim 28 wherein the gas release linefrom said second outlet is provided with an analyzer for analyzing gasevaporated from said flash vessel.
 30. The system of claim 26 furthercomprising a controller for sequentially operating said sample inputvalve and said sample release valve in said sample conduit in a sequencein which said sample input valve is open while sample release valve isclosed followed by a sequence in which said sample release valve is openwhile said sample input valve is closed.
 31. The system of claim 25wherein said sample receiving chamber has a purge gas inlet line for theintroduction of a purge gas into said sample receiving chamber and apurge gas outlet line for the recovery of purge gas.
 32. The system ofclaim 31 wherein said sample receiving chamber is provided with a filterinterposed between the interior of said sample release chamber and thepurge gas outlet line from said sample release chamber.
 33. The systemof claim 32 further comprising a collection vessel connected to saidpurge gas outlet line.
 34. The system of claim 25 wherein the sampletransfer line extending from said flash tank to said sample receiver isprovided with a first outlet valve in proximity to said flash tank and asecond outlet valve spaced from and connected in series with said firstoutlet valve.
 35. The system of claim 34 wherein the sample transferline from said flash tank is provided with a flow controller forsequentially operating said first and second outlet valves in which saidfirst valve is opened while maintaining said second valve closed andthereafter closing said first valve while opening said second valve forthe transfer of polymer sample from said flash tank to said samplereceiving vessel.
 36. The system of claim 34 wherein said flash tank isprovided with a heater for heating the contents of said flash tank. 37.The system of claim 34 further comprising a second sample receivingchamber in parallel with said first recited sample receiving chamber andfurther comprising a diverter valve in said sample transfer lineconnected downstream of said second outlet valve for alternativelyconnecting the outlet of said flash chamber to one of said samplereceiving chambers while retaining the other said sample receivingchamber offstream.
 38. The system of claim 37 further comprising a purgeline interconnected to said sample transfer line between said outletvalves and the said diverter valve.
 39. The system of claim 25 furthercomprising a second polymerization reactor and a polymer transfer linefor the transfer of polymer slurry from said first reactor to saidsecond reactor, said second reactor further comprising a sampling systemas recited in subparagraphs b) through f) of claim
 25. 40. The system ofclaim 39 further comprising a settling leg connected to said secondreactor for recovery of polymer slurry from said second reactor, apolymer outlet line extending from said settling leg to a flash recoveryvessel having a first outlet for removal of gas therefrom and a secondoutlet for the transfer of polymer particles and a purge vesselconnected to said second outlet for the recovery of polymer particlesfrom said flash recovery vessel.